(i) Field of the invention
The present invention relates to a dyestuff for heat-sensitive transfer record (hereinafter abbreviated to "sublimable dyestuff"), an ink composition for heat-sensitive transfer record and a transfer sheet which can be used in color hard copies and the like utilizing a sublimation heat transfer record system.
(ii) Description Prior Art
A heat transfer record system using a sublimable dyestuff is one of the heat transfer print systems which comprise forming a transfer sheet by coating a thin condenser paper or PET film having a thickness of several microns with an ink of a sublimable dyestuff, and then selectively heating the transfer sheet by means of a heat-sensitive head to transfer the dyestuff to a record paper which is a material to be recorded. Nowadays, the heat transfer record system has been used as a means for the image record (hard copy) of much image information.
The sublimable dyestuffs which are used in the present invention are required to have abundant colors and strong adhesive force, and to be excellent in color mixing properties and stability. In the above-mentioned record system, the amount of the dyestuff to be sublimated depends upon heat energy, and so the density of the transferred dyestuff can be analogically controlled. This is a major feature which other printing systems cannot possess.
As yellow sublimable dyestuffs, there are quinophthalone compounds having excellent light resistance and fastness (Japanese Patent Laid-open Nos. 53565/1985, 18928-9/1988 and 182192/1988), but most of these dyestuffs lack both of a high sublimation speed and the stability of a transferred image. The development of dyestuffs which can meet the optimum requirements of sublimable dyestuffs has been sought.